The present invention relates to a method for the manufacture of an electromagnetic actuator, especially of an actuator for the actuation of a charge cycle valve of an internal combustion engine.
German Published Patent Application No. 197 12 056 describes an electromagnetic actuator, especially for the actuation of a charge cycle valve of an internal combustion engine. The actuator includes two opposing electromagnets and a rotary armature reciprocating between them, which when the magnets are de-energized is held by spring forces in an intermediate position between the electromagnets, and when one of the electromagnets is energized is brought into a limit position in proximity to the pole faces of the corresponding electromagnet. The rotary armature is connected to the part to be driven, in this case the stem of the charge cycle valve, so that opening and closing of the valve can be performed by alternating actuation of the electromagnets.
The energy needed by the closing magnet and the opening magnet, also referred to as catching energy, in order to attract the rotary armature from a certain distance increases exponentially with the distance. Furthermore, the greater the gap between the attracted rotary armature and the pole face of the activated electromagnet, the greater the holding energy needed to hold the rotary armature in the open or closed position. In order to minimize the efficiency losses, therefore, the pole faces of the electromagnets must be oriented very accurately in relation to the swivel axis of the rotary armature, so that in operation the contact face of the rotary armature bears as accurately as possible on the pole face of the electromagnet activated at any time. This result can be achieved only by a high dimensional stability of the individual components of the actuator and by a highly accurate orientation of the individual elements in relation to one another. The associated expenditure for machining and assembly is extremely high, resulting in considerable costs. Furthermore, the many positional and angular parameters that have to be taken into account present an extremely complex assembly problem, which renders series production of such actuators virtually unfeasible.
It is therefore an object of the invention therefore is to propose a method of assembly for the manufacture of actuators, which is unsusceptible to production inaccuracies of individual components and which at the same time minimizes the efficiency losses in operation.
The above and other beneficial objects of the present invention are achieved by providing a method as described herein.
According to one example embodiment of the present invention, the electromagnet is first inserted loosely into an actuator frame, in relation to which the swivel axis of the rotary armature is fixed by way of bearing points. The electromagnet is then brought into a defined operating position in relation to the rotary armature. In this spatial and angular position of the electromagnet relative to the rotary armature, the electromagnet is permanently fixed in relation to the frame, so that the spatial and angular position of the electromagnet in relation to the frame is fixed. As a result, the electromagnet is consequently also selectively connected in relation to the swivel axis of the rotary armature, fixed to the frame.
The defined operating position of the electromagnet may be adjusted in relation to the rotary armature by passing a current through the electromagnet. If a current is passed through the electromagnet, a force field is built up between the pole face of the electromagnet and the contact face of the rotary armature arranged opposite the pole face, the force field pulling the electromagnet into a spatial and angular position relative to the rotary armature that is advantageous from various energy standpoints. In this relative position, the electromagnet is oriented in relation to the rotary armature so that the contact face of the rotary armature bears on the pole face of the activated electromagnet, minimizing the intermediate air gap. This arrangement therefore corresponds to the desired orientation between electromagnet and rotary armature, in which efficiency losses in the operating condition may be minimized. The electromagnet is permanently fixed in this spatial and angular position in relation to the frame, so that the spatial and angular position of the electromagnet relative to the frame, assumed while a current was being passed through, is fixed. As a result, the electromagnet is therefore also fixed in relation to the swivel axis of the rotary armature, fixed to the frame, so that the meeting between the pole face of the electromagnet and the contact face of the rotary armature is optimized from the energy standpoint when a current is passed through the electromagnetxe2x80x94and hence in the operating condition of the actuator.
At the same time, this positional and angular orientation and subsequent fixing of the electromagnet relative to the rotary armature is achieved entirely regardless of production inaccuracies of these two components. There is a single reference point in assembling the electromagnet, and this reference point is defined solely by the orientation of the pole face, which bears against the contact face of the rotary armature. All other dimensions of the electromagnet play no part in this reference point and may therefore contain, e.g., production, inaccuracies. It is also possible through orientation of the electromagnet on the contact face of the rotary armature, to compensate for any positional inaccuracies of the swivel axis of the rotary armature in the frame. The method according to the present invention therefore permits a considerable reduction in production costs, since expensive machining of selected strike faces and assembly faces is no longer necessary for highly accurate orientation of the electromagnet. This arrangement obviates the need for a precise dimensional stability of components, and a reduction in production costs may be achieved through the avoidance of fine production tolerances and linked series of tolerances.
Furthermore, the method includes only a few, simple stages. It is therefore cost-effective and suitable for mass production. Finally, the method ensures that assembly is performed under realistic operating conditions (biasing of the rotary armature, opening and closing positions of the valves). That is, the electromagnet is fixed in a position relative to the rotary armature such that the rotary armature in subsequent operational service bears virtually free of distortion on the pole face of the electromagnet when a current is passed through the electromagnet. This arrangement reduces the bending load on the rotary armature and increases its service life considerably. The efficiency of the actuator system may be increased and its energy demand considerably reduced by the method of assembly according to the present invention, so that the actuator cooling system needs to meet lower requirements or may be eliminated.
The method described above for fixing a single electromagnet in an actuator may easily be extended to actuators with two electromagnets, the pole faces of which at least partially face one another. In this case, two electromagnets are first arranged loosely in the actuator frame, in relation to which the swivel axis of the rotary armature is fixed by way of bearing points. The rotary armature is then brought into a first defined operating position and fixed in this position. By passing a current through the first electromagnet (i.e., that corresponding to this operating position), this electromagnet is brought into the most favorable spatial and angular position from the energy standpoint corresponding to this operating position and in this position is fixed in relation to the frame. The rotary armature is then brought into a second defined operating position and is temporarily fixed in this position. By passing a current through the second electromagnet (i.e., that corresponding to the second operating position), this second electromagnet is brought into a spatial and angular position, which corresponds to a minimization of the gap between the pole face of the second electromagnet and the contact face of the rotary armature opposite the pole face, and in this position is fixed in relation to the frame. In the method according to the present invention, therefore, the positioning and fixing of each electromagnet is performed in isolation from the other electromagnet. The costly and error-prone simultaneous assembly of both electromagnets necessary in conventional production methods is therefore eliminated.
In order to achieve the minimum possible deformation of the electromagnets and of the frame during fixing of the electromagnet and thereby to obtain an assembled state that is as stress-free as possible, the electromagnet may be fixed by a low-distortion joining method. The use of laser welding has proved particularly advantageous in this context, since it ensures a rapid joining of the two joined parts with localized, strictly limited heat input.
With regard to the actual form of the joint area between electromagnet and frame, the electromagnet may be provided with a protruding stud, which in the actuator assembly position projects through an opening in the wall of the frame into the outer chamber. When a current is passed through the electromagnet as described above, the stud fixed to the magnet assumes a certain spatial and angular position, in which it must be fixed in relation to the frame. This fixing is achieved by a fixed connection of the end of the stud projecting outwardly through the frame wall to the frame. The actual joint area may thereby be situated in the outer area of the actuator, which considerably improves the visibility and accessibility of the joint, thereby substantially facilitating the joining process.
In order to avoid distortions of the rotary armature the opening in the frame wall, through which the end of the stud is fed, must be designed with sufficiently large dimensions so thatxe2x80x94irrespective of the production inaccuracies of the components to be assembledxe2x80x94the stud may be fed through the opening unimpeded without touching the edges of the opening when a current is passed through the electromagnet. In the energized state of the electromagnet there is therefore a peripheral gap between the stud and the edges of the opening that has to be bridged by the joining process. To bridge this gap, a connecting element may be used, which bears flatly on the frame. The connecting element is first positioned without a gap in relation to the stud and joined to the stud. The connecting element is then joined to the frame in the overlap area. This arrangement allows the stud end to be fixed in any spatial and angular position in relation to the frame opening.